1. Field of the Invention
The present invention relates to a charged particle beam apparatus, and more particularly, to a technique for measuring the shape and dimensions of a circuit pattern formed on a specimen or inspecting the circuit pattern.
2. Description of the Related Art
A technique for inspecting or reviewing the state of a circuit pattern formed on a semiconductor wafer is important to improve the yield and reliability of the products. The inspection or review is performed by an apparatus using light or an apparatus using charged particle beams, such as electron beams. In particular, in recent years, with the size reduction of semiconductor devices, the inspection and review processes using charged particle beams have become important. However, the surface of the semiconductor wafer during a manufacturing process is formed of an insulating film, such as a silicon oxide, a silicon nitride, an organic material, or a high-k material. Therefore, when a charged particle beam is radiated onto the surface of the wafer, the surface of the wafer is electrified, which changes the trajectory of signal particles generated from the surface. Particularly, the change in the trajectory of the signal particles is noticeable at the boundary between an area in which the charged particle beam is radiated and an area in which no charged particle beam is radiated, that is, at the boundary between a charged-up area and a neutron area. As a result, an image error, such as brightness variation, occurs in an acquired image formed by the signal particles. In addition, the image error, such as the brightness variation, may occur at the center of the acquired image due to the relationship between the structure or arrangement of a pattern and the scan direction of the charged particle beam. Since this image error deteriorates inspection accuracy, it is important to reduce the image error.
As an example of the technique for reducing the image error, Japanese Unexamined Patent Application Publication (JP-A) Nos. 2004-227886 and 11-120951 disclose a technique that scans an area larger than a display area of an acquired image with an electron beam to acquire an image and trims out a necessary area from the acquired image. In addition, as a technique for avoiding the influence of a contrast variation caused by the arrangement of a pattern, JP-A No. 2003-303564 and JP-A No. 2005-285746 disclose a technique that radiates an electron beam in a direction that is inclined at a predetermined angle in the plane with respect to the scan direction of the electron beam when an image is captured, thereby performing auto-focus.